Juno to Risk Jupiter’s Fireworks for Science

On July
4, NASA will fly a solar-powered spacecraft the size of a basketball court within
2,900 miles (4,667 kilometers) of the cloud tops of our solar system’s largest
planet.

As of
Thursday, Juno is 18 days and 8.6 million miles (13.8 million kilometers) from
Jupiter. On the evening of July 4, Juno will fire its main engine for 35
minutes, placing it into a polar orbit around the gas giant. During the flybys,
Juno will probe beneath the obscuring cloud cover of Jupiter and study its
auroras to learn more about the planet's origins, structure, atmosphere and
magnetosphere.

"At this time last year our New Horizons
spacecraft was closing in for humanity’s first close views of Pluto,” said
Diane Brown, Juno program executive at NASA Headquarters in Washington. “Now,
Juno is poised to go closer to Jupiter than any spacecraft ever before to
unlock the mysteries of what lies within.”

A series
of 37 planned close approaches during the mission will eclipse the previous record
for Jupiter set in 1974 by NASA’s Pioneer 11 spacecraft of 27,000 miles (43,000
kilometers). Getting this close to Jupiter does not come without a price -- one
that will be paid each time Juno's orbit carries it toward the swirling tumult
of orange, white, red and brown clouds that cover the gas giant.

"We
are not looking for trouble, we are looking for data," said Scott Bolton,
principal investigator of Juno from the Southwest Research Institute in San
Antonio. "Problem is, at Jupiter, looking for the kind of data Juno is
looking for, you have to go in the kind of neighborhoods where you could find
trouble pretty quick."

The
source of potential trouble can be found inside Jupiter itself. Well below the
Jovian cloud tops is a layer of hydrogen under such incredible pressure it acts
as an electrical conductor. Scientists believe that the combination of this
metallic hydrogen along with Jupiter's fast rotation -- one day on Jupiter is
only 10 hours long -- generates a powerful magnetic field that surrounds the
planet with electrons, protons and ions traveling at nearly the speed of light.
The endgame for any spacecraft that enters this doughnut-shaped field of
high-energy particles is an encounter with the harshest radiation environment
in the solar system.

"Over
the life of the mission, Juno will be exposed to the equivalent of over 100 million
dental X-rays," said Rick Nybakken, Juno's project manager from NASA's Jet
Propulsion Laboratory in Pasadena, California. "But, we are ready. We
designed an orbit around Jupiter that minimizes exposure to Jupiter’s harsh
radiation environment. This orbit allows us to survive long enough to obtain
the tantalizing science data that we have traveled so far to get.”

Juno's
orbit resembles a flattened oval. Its design is courtesy of the mission's
navigators, who came up with a trajectory that approaches Jupiter over its
north pole and quickly drops to an altitude below the planet's radiation belts
as Juno races toward Jupiter's south pole. Each close flyby of the planet is
about one Earth day in duration. Then Juno's orbit will carry the spacecraft
below its south pole and away from Jupiter, well beyond the reach of harmful
radiation.

While
Juno is replete with special radiation-hardened electrical wiring and shielding
surrounding its myriad of sensors, the highest profile piece of armor Juno
carries is a first-of-its-kind titanium vault, which contains the spacecraft's
flight computer and the electronic hearts of many of its science instruments.
Weighing in at almost 400 pounds (172 kilograms), the vault will reduce the
exposure to radiation by 800 times of that outside of its titanium walls.

Without
the vault, Juno’s electronic brain would more than likely fry before the end of
the very first flyby of the planet. But, while 400 pounds of titanium can do
magical things, it can't do it forever in an extreme radiation environment like
that on Jupiter. The quantity and energy of the high-energy particles is just
too much. However, Juno’s special orbit allows the radiation dose and the
degradation to accumulate slowly, allowing Juno to do a remarkable amount of
science for 20 months.

“Over the
course of the mission, the highest-energy electrons will penetrate the vault,
creating a spray of secondary photons and particles,” said Heidi Becker of JPL,
Juno’s Radiation Monitoring Investigation lead. “The constant bombardment will
break the atomic bonds in Juno’s electronics.”

JPL manages the Juno mission for the principal investigator,
Scott Bolton, of Southwest Research Institute in San Antonio. Juno is part of
NASA's New Frontiers Program, which is managed at NASA's Marshall Space Flight
Center in Huntsville, Alabama, for NASA's Science Mission Directorate. Lockheed
Martin Space Systems, Denver, built the spacecraft. The California Institute of
Technology in Pasadena manages JPL for NASA.